This invention relates to a method for evaluating the effectiveness of inspection penetrants. In a more particular aspect, this invention relates to a method and testing panel for ascertaining the flaw detection capabilities of fluorescent inspection penetrants.
The inspection of metal products in order to determine their conformance to predetermined standards of quality is of critical importance in the metal fabrication industry. The inspection and detection of flaws generally takes the form of visual testing or the utilization of various test instruments such as x-ray machines necessity for establishing a reliable and economical testing procedures is common to all product manufacturing. It is especially necessary in the fabrication of metal castings and machine parts which are often characterized by surface flaws and defects. Shrinkage cavities, microcracks blowholds and the like are not readily discernable by visual inspection. Consequently, industry has developed a testing method which utilizes various types of penetrating solutions for detecting such flaws. Usually, the penetrant is applied to the surface of the metal part. The solution is then washed or wiped off the surface to remove excess penetrant. Sufficient time is allowed to lapse in order to allow the penetrant to seep to the surface. The penetrant agent can then be detected visually by its color or luminescence.
The penetrant inspection method obviously provides a reliable and economical method of testing. As a result, a considerable research effort has been generated in an attempt to provide penetrants which are even more economical, more efficient and useful for particular or specific testing situations. The evaluation of solutions as candidates for a penetrating inspection procedure often becomes time consuming and expensive. Therefore, a simple and economical means for evaluating penetrant solutions evolved through the use of test panels having surface cracks and defects of known dimension. Various types were fabricated and one of the earliest was the heated aluminum block in which cracks were induced by sudden quenching in ice water.
Another type developed was the chrome-cracked plate in which a sheet of copper is plated with layers of nickel and chromium in specific thicknesses. Since the chrome layer is brittle, cracks are easily induced. Still another type of cracked test panel was constructed by plating a soft metal such as copper with a brittle metal, such as iron. In the utilization of all of these test panels, the cracks are generated in the brittle surface by bending the panel over a curved form or arbor, and then straightened or flattened. The straightening process, however, tends to close up the surface cracks so that their width is on the order of 0.1 micron or less. In order to provide an effective and useful test panel, rigid controls under strict laboratory conditions were required. This resulted in an added expense to the testing procedure. With the present invention, however, it was found that the problems encountered in using rigid controls and stringent laboratory conditions could be avoided by fabricating the panels from spring steel having an electroless coating of nickel. The resulting panel provides an efficient testing device for fluorescent penetrants. It is considerably more sensitive than the previously used cracked aluminum block and can be fabricated on a production basis without the need for expensive laboratory controls and conditions.